1. Field of the Invention
The invention relates, generally speaking, to optoelectronic switching networks intended, in wide-band cabled telecommunications systems, for switching the modulated signals of one incoming channel in a plurality of incoming channels over to one outgoing channel in a plurality of outgoing channels.
The wide-band telecommunications systems involved herein are of the "multi-service" type in that they permit:
the diffusion of motion picture programs to subscribers from television stations and video-broadcasting stations (video-libraries in particular) as well as the transmission of information to these stations (calls, opinion surveys, etc. . . . ) from subscribers, such diffusion then being called "inter-active";
the transmission of data to subscribers at their request from administrative bodies, service distributors, data banks, etc. . . . ;
telephone and videophone communication between subscribers; etc. . . .
2. Description of the Prior Art
The type of known optoelectronic switching networks to which the invention applies comprises:
an emitter board including an assembly of light emitting optoelectronic units termed "emitter units" which are connected to incoming channels and which emit modulated light signals the intensity of which reproduces the modulation of the signals routed via the said incoming channels;
a receiver board including an assembly of light receiving optoelectronic units termed "receiver units" all of which can be illuminated by the emitter board and which transmit signals to outgoing channels where the intensity of such signals reproduces the modulation of at least one light signal among those to which the said receiver units are exposed.
For at least one given incoming channel to be switched to at least one given outgoing channel, units referred to as "selector units" are provided in one of the emitter or receiver boards, the board which comprises the selector units being referred to as "selector board". Each selector unit comprises an array of elementary optoelectronic components (light receivers or emitters depending on the case) referred to as multi-cells equal in number to the number of units (light emitters or receivers depending on the case) referred to as "conjugated units" of the other board referred to as "conjugated board", optical means providing optical conjugation of at least one of the cells with one of the conjugated units and selection means making it possible to switch at least one cell onto one channel of the said selector unit.
A known optoelectronic switching network of this nature may belong to one or to the other of two categories.
In an optoelectronic switching network falling into the first category, known in particular through U.S. Pat. No. 4,437,190 (FIGS. 1-14, inclusive), the selector board is the receiver board. The receiver units of the said receiver board are termed "multi-cell receivers". The receiver cells which form the receiver units are for instance photodiodes. The conjugated units in the conjugated emitter board are for instance light emitting diodes or laser diodes.
In an optoelectronic switching network coming under the second category, known in particular through U.S. Pat. No. 4,437,190 (FIGS. 15-26 inclusive), the selector board is the emitter board. The emitter units of the said board are termed "multi-cell emitters". The emitter cells from these multi-cells emitters are for instance light emitting diodes or laser diodes. The conjugated units in the conjugated receiver board are for instance photodiodes.
Whatever the category under consideration, it is advantageous for the array of conjugated units in the conjugated board to form a matrix, i.e. that these conjugated units lie in rows and columns. Indeed, this lay-out makes it possible to arrange the cells of each selector unit of the selector board in matrix form and therefore to simplify the design of the selection means in the said selector unit since to optically activate a cell to be switched to the channel associated with the said selector unit cell, it is sufficient to select the row and column to which it belongs. The lay-out of the selector units into random-access matrix-form integrated circuits in which the selection means are themselves advantageously integrated, is thereby greatly eased.
Furthermore, whatever the category being considered, the incoming or outgoing signals can be electrical, in which case the channels are for example coaxial cables, or optical, in which case the channels are optical fibers. Whether the signals are electrical or optical, they can be in analog or digital form. Lastly, they can be multiplexed.
To conclude, whatever the category being considered, these optoelectronic switching networks of the known type are able to build up several simultaneous communications from different calling parties to different called parties. However, they are unable to build up several simultaneous communications between one and the same calling party and plural called parties and several simultaneous communications between plural calling parties and one and the same called party. This is because the selector unit has only one access (input or output) per subscriber.